The invention relates to an arrangement for controlling the air flow over aerodynamic profiles. Such arrangements for controlling the air flow past aerodynamic profiles by the discharge of fluids through orifices which are spaced apart along the length of the profile transversely to the air flow past the profile for the avoidance of boundary layer separation are known. In the known arrangements the orifices are slots extending substantially over the whole length of the profile and through which the fluids are exhausted. The discharge is effected with great energy. Thus it is attempted to increase the velocity of the air-flow in the layer near to the skin by an input of energy, and thereby to eliminate the risk of separation. (Aerodynamik des Flugzeuges-(Aerodynamics of Aircraft) by Schichtling and Truckenbrodt, Vol. 1, pp. 260-263, Springer Verlag, 1959).